Commentary on Hemosiderin.

By G. W. RIciiTER AND M. C. BEssIs T HE TERM HEMOSIDERIN (“H#{228}mosiderin”) was proposed by Neumann1 though others had earlier recognized the material to which the word refers, notably Perls.2 Neumann’s definition was clearly based on histologic and histochemical criteria : brown granules giving certain reactions for iron, particularly the Prussian ( Berlin ) blue test, as seen in situ in cells or tissues through the light microscope. Later microscopists have confirmed and extended the observations of Neumann. The advent of electron microscopy has led investigators to inquire into the fine stnicture of the granules described by the earlier histologists and histochemists. For this purpose material has been examined in situ in cells as well as after isolation from cell homogenates.411 Some of the findings and conclusions are summarized in this brief report. As seen in situ in cells, typical, Prussian-blue-positive hemosiderin granules occur in at least five forms: ( 1 ) Closely packed cytoplasmic collections of particles of high electronscattering power, ranging from about 8 A to about 70 A in diameter. The collections are often, but not always, enclosed in single ( unit ) cytoplasmic membranes. Sometimes there is more than one enveloping membrane. Many of the particles can be identified as the ( FeOOH ) micelles of individual ferntin molecules; these have characteristic size, shape and subunits, as first shown by Farrant’2 Other particles in the aggregates are clearly not parts of fernitin molecules (figs. 1, 2) . Electron diffraction studies have indicated that they are forms of Fe2O3, mainly a-Fe2O3.H2O. The cytoplasmic bodies as a whole vary greatly in size ( up to several microns in diameter). (2) Closely packed cytoplasmic collections of dense particles without admixture of ferritin molecules, but otherwise similar to those described in ( 1). These also are commonly enclosed in single unit membranes. (3) More complex bodies in which material such as that found in the first and second types are mixed with osmiophilic substances (presumably lipids or “lipofuscin” ) or with other material of moderate electron-scattering power. These bodies sometimes contain myelin figures or other membranous cornplexes and have single or multiple unit membranes at their peripheries. Such compound bodies are included in the categories others have termed lysosomes, cytolysomes, cytosomes etc. This type is frequently encountered in hepatic parenchymal cells in cases of hemochromatosis. (4) Crystals of fernitin with characteristic structure and lattice spacings.